2007/10/24, Dieter <[EMAIL PROTECTED]>: > > > > Will OGC be able to output arbitrary waveforms, or only video? > > > If OGC can generate sine waves, square waves, triangle, etc. > > > it would be very useful as a piece of test equipment. It > > > could be a tracking generator for the spectrum analyzer? > > > > I thought it would be interesting to generate RF signals entirely in > > the digital domain and use a video DAC to turn it into analog. For > > instance, you can have a sine-wave generator, that's completely > > digital, and it has parameters that you can use to adjust the > > frequency, within a band. BOOM. You have an FM transmitter. Attach > > an amplifier, and you can send audio to a nearby radio. > > > > Say we could do this where we mix a complete TV signal, on channel > > 3/4, video with color subcarrier, and the audio channel. Voila. No > > more need for a TV chip, and we can get both s-video and encoded. > > > > If the granularity of our control of the signal is 330Mhz, can we > > encode all of the information in the TV signal? Would the steps > > between digital levels (1024 of them) be too noisy? Could we fix that > > with a low-pass filter? > > Are there any roadblocks that would prevent OGC from being an ATSC > modulator? E.g. take a mpeg2ts file on disk, and output it as > ATSC modulated on channel 3 or 4 on RG6QS and feed that into a > digital television or one of the inexpensive ATSC-to-NTSC boxes > that are supposed to magically appear before the analog transmissions > stop on 2009-02-17. > > If this works, we wouldn't need to decode the mpeg. We could have > the noisy DVR computer in another room and use inexpensive RG6QS to > get the signal to the TV. Since this is digital, we wouldn't have > the loss of quality that analog modulators give. > > Anyone have an idea of how much CPU power it would take to do this > modulation? Is this something the GPU could do? > > For Europe (and most of the world), I believe the substitution is > /ATSC/DVB-T/ ?
On the signal side it would be possible to generate the signal to transmit at the correct IF for receiving by a receptor on channel 3 or 4. It's a simple AM modulation fundamentally. There would be the question about making the DAC work at a frequency that is an integer multiple of the digital data stream (bit rates + sync+ other) for correct transmition and dodging possible problem. There would be barely enough definition in the output DAC to be able to generate a correct signal, but still doable. The last stage(digital) for the encoding would require a DDS who would generate the output sinus, before multiplying with the baseband signal, absolutely an hardware implementation. For the preprocessing required to encode in the 8VSB format some part would need to be made in hardware for synchronization purpose. Software just couldn't keep up at this sort of continuous data rates. Also after outputting the signal there would be a need for a 6MHz cut-band filter to filter the unnecessary signal image and respect the channel frequency. So a GPU would probably not be able to pull it off. A carefully design FPGA could possibly make it but there would still be some heavy work to be done by a cpu to organise the data as required for transmition. A special adaptor would be required between the connector and the communication channel used.
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